1. Field of the Invention
The present invention generally relates to a security arrangement for, and a method of, protecting from unauthorized disclosure a private security code used for rendering microprocessor-controlled electronic equipment operational.
2. Description of Related Art
U.S. Pat. No. 4,494,114 disclosed a lock-out security arrangement for and method of maintaining microprocessor-controlled electronic equipment normally operational until the occurrence of a disabling event and, thereupon, for rendering the equipment inoperative after the occurrence of the disabling event and for maintaining the equipment inoperative even after the disabling event has terminated until a private security code has been entered via a keyboard to the equipment microprocessor. In one particularly advantageous application, the equipment was a radio installed in an automobile dashboard, in which case, the disabling event was a theft which can be detected, for example, by sensing an interruption of power from the automobile battery, or by sensing the physical removal of the radio from the dashboard.
In said patent, the user selected and remembered the private security code. The stolen equipment was essentially valueless to a thief, because the equipment remained inoperative until the private security code was entered to the microprocessor. Inasmuch as the private security code was just that, i.e. secret and selected by, and known only to, the user, there was no way for the thief to obtain the code. The thief could not physically or electronically interrogate the microprocessor to learn the code, because the code was stored in an internal, non-volatile memory, e.g. a read/write random access memory with a battery back-up circuit, or an electrically erasable programmable read only memory, accessed solely from within and, hence, protected from external interrogation.
Although very satisfactory for its intended purpose, the patented lock-out arrangement and method can be implemented in another mode which does not require the user to select, remember, change or otherwise use any private security code. It would be desirable in certain applications if system security did not depend on a user having a forgetful memory. Also, in the event that a user was threatened by a thief to divulge the private code, it would be desirable, in terms of system security, if the user did not know the private code.
Other security systems of which we are aware include U.S. Pat. Nos. 4,139,864; 4,495,540; 4,318,005; 4,347,545 and 4,267,578.